The potential impact of climate change on the Schizophoran flies of Australia's wet tropics rainforests
Date
2010
Authors
Wilson, Rohan David
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The world's climate is expected to change profoundly and rapidly over the course of this century, and biologists have turned their attention towards predicting the effects that these changes are likely to have on living systems. This has invariably brought us back to fundamental ecological questions that remain unanswered for most taxa: how are species distributed in space and time? How is diversity distributed? What is the relationship between these patterns and climate, including extreme events? There is a particularly urgent need to answer these questions for tropical rainforest invertebrates, which represent a high proportion of global biodiversity but remain poorly known. This thesis attempts to answer these questions for one such group, focusing on schizophoran flies, which represent nearly two thirds of dipteran species richness, in Australia's Wet Tropics rainforests. Over the course of this century, Australia's tropical rainforests are expected to experience higher temperatures, longer and drier dry seasons, and more powerful cyclones. Based on the analyses in this thesis, these changes would likely result in large changes to the schizophoran community. Increased temperature will likely result in rapid shifts, contractions, and fragmentation of species distributions. Increased dry season severity will likely reduce local abundances and diversities, and while Schizophora may be resilient to more powerful cyclones in the short-term, the longer-term consequences are unknown. These climatic changes are likely to result in a significant loss ofbiodiversity in the Australian Wet Tropics bioregion. Enough data were collected to give robust estimates of abundance and diversity across a range of sub-regions and altitudes in Australia's Wet Tropics rainforests. Altogether, 49,231 individuals were collected from 7,036 trap-days, and 542 morphospecies. Climatic variables were used to model both the local diversity of species and local abundances, particularly in the dry-season. As would be predicted by energy-richness theories, warm lowland areas that stay wet over the dry season have the most abundant and diverse communities, whereas lowland areas that dry out and highland areas which are cool have lower diversities/abundances. The structure of those communities, and which species they include, appears to be heavily dependent on temperature and rainfall seasonality. The distributions of a large subset of species were also spatially modelled, and these models suggest that temperature appears to play a key role in determining species distributions. Even small increases in temperature (1~2{u00B0}C) are expected to result in greatly diminished ranges, and with larger increases (3-5{u00B0}C) a high proportion of species (nearly half) are predicted to go extinct. Levels of predicted extinctions presented in this thesis are in broad agreement with similar studies of species distributions from around the world. Cyclone Larry caused massive changes to certain resources on one of the studied transects in 2006, and schizophoran functional guilds associated with these resources responded accordingly. However, the schizophoran community was surprisingly resilient to this disturbance, returning to a 'pre-cyclone' community within only 18 months of the cyclone impact. All of the above results are consistently repeated throughout the dataset and for each major family if analysed separately.
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